Unity is part of the Ayatana project, an initiative to improve the user experience within Ubuntu.[9] In addition to Unity, there are Application Indicators and other projects such as MeMenu, the notification system and the application NotifyOSD gathered.

Top menu bar – a multipurpose top bar, saving vertical space, and containing: (1) the menubar of the currently active application, (2) the capture bar of the main window of the currently active application including the maximize, minimize and exit buttons, (3) the global system pulldown menu including the global system settings, logout, shut down and similar basic controls, and (4) the diverse global notification indicators including the time, weather, and the state of the underlying system.[10]

Launcher – a dock that also serves as a window switcher. Multiple instances of an application are grouped under the same dock icon, with a number of indicators to the side of the icon showing how many instances are open.[11]

Quicklist – the accessible menu of launcher items.

Dash – an overlay that allows the user to search quickly for information both locally (installed applications, recent files, bookmarks, etc.) and remotely (Twitter, Google Docs, etc.) and displays previews of results.[12] The Dash search feature was the subject of the privacy controversy.

Head-up display (HUD) – introduced with Ubuntu 12.04. It allows hotkey searching for top menu bar items from the keyboard, without the need for using the mouse, by pressing and releasing the Alt key.[13]

Indicators – a notification area (similar to an OS Xmenu extra), containing displays for the clock, network and battery status, sound volume etc.

Video lens is a lens to search videos from the user's video library and online video services such as YouTube.

Social lens is a lens to find the user's SNS activities such as Twitter, Facebook and Google+ (via the Unity online account function).

Shopping lens is a lens for online shopping. It shows Amazon.com search results in the Dash home lens. However, this lens takes search queries from all lenses. See Privacy controversy. The shopping lens is filtered to prevent the loading of pornographic images.[14][15]

Unity 2D showing the ability to run alongside different window managers and desktop environments

Canonical maintained two discrete versions of Unity, which are visually almost indistinguishable but technically different.

Unity is written as a plugin for Compiz[19] and uses an uncommon OpenGL toolkit called Nux.[5] Being a plugin for Compiz gives Unity GPU-accelerated performance on compatible systems. It is written in the programming languages C++ and Vala.

Unity 2D is a set of individual applications[20] developed for environments that Compiz does not run on, such as when graphics card does not support OpenGL. They are written in the GUI building language QML from the widespread Qt framework.[21] By default Unity 2D uses the Metacity window manager[20] but can also use accelerated window managers like Compiz or KWin. In Ubuntu 11.10, Unity 2D uses Metacity's XRender-based compositor to achieve transparency effects.[citation needed] Starting with Ubuntu 11.10, Unity 2D replaced the classic GNOME Panel as the fall-back for users whose hardware cannot run the Compiz version of Unity.[22]

Unity 2D was discontinued for the release of Ubuntu 12.10 in October 2012, as the 3D version became more capable of running on lower-powered hardware.[23]

As Unity and the supporting Ayatana projects[24] are developed primarily for Ubuntu, Ubuntu is the first to offer new versions.

Outside of Ubuntu, other Linux distributors have tried to pick up Ayatana, with varying success. The Ayatana components require modification of other applications, which increases the complexity for adoption by others.

Arch Linux offers many Ayatana components, including Unity and Unity 2D, via an unofficial repository or through AUR.[25]

Fedora does not offer Unity in its default repositories because Unity requires unsupported patches to GTK.[26] However Unity 6 has been ported to Fedora 17 and can be installed through a branch in the openSUSE repositories where the patches are applied.[27] Newer Fedora and Unity versions are not supported.[28]

Frugalware had adopted Ayatana, including Unity and Unity 2D, as part of the development branch for an upcoming Frugalware release but the project is no longer maintained.[29]

openSUSE offers many Ayatana components for GNOME.[30] After the packager abandoned the project because of problems with the then-current version of Compiz,[31] new developers picked up the task and provide packages for openSUSE 12.2 (along with versions for Arch Linux and Fedora 17). Newer openSUSE and Unity versions are not supported.[28]

In November 2010, Ubuntu Community Manager Jono Bacon explained that Ubuntu will continue to ship the GNOME stack, GNOME applications, and optimize Ubuntu for GNOME. The only difference, he wrote, would be that Unity is a different shell for GNOME.[33]

Canonical announced it had engineered Unity for desktop computers as well and would make Unity the default shell for Ubuntu in version 11.04.[34]

GNOME Shell was not included in Ubuntu 11.04 Natty Narwhal because work on it was not completed at the time 11.04 was frozen, but is available from a PPA,[35] and is available in Ubuntu 11.10 and later releases, through the official repositories.[36]

In November 2010, Mark Shuttleworth announced the intention to eventually run Unity on Wayland instead of the currently used X window system,[37] although this plan has since been dropped, replacing Wayland with Mir for Unity 8.[38]

In December 2010, some users requested that the Unity launcher (or dock) be movable from the left to other sides of the screen, but Mark Shuttleworth stated in reply, “I'm afraid that won't work with our broader design goals, so we won't implement that. We want the launcher always close to the Ubuntu button.”[39] However, with Ubuntu 11.10, the Ubuntu button has been moved into the launcher, rendering this argument invalid. A third-party plugin that moves Unity 3D's launcher to the bottom is available.[40]

As of 2010[update], the Unity shell interface developers use a toolkit called Nux instead of Clutter.[41] Unity is a plugin of the Compiz window manager,[5] which Canonical states is faster than Mutter,[42] the window manager for which GNOME Shell is a plugin.

On 14 January 2011, Canonical also released a technical preview of a “2D” version of Unity based on Qt and written in QML.[21] Unity-2D was not shipped on the Ubuntu 11.04 CD, instead the classic GNOME desktop was the fall-back for hardware that could not run Unity.[43][44]

In March 2011, public indications emerged of friction between Canonical (and its development of Unity) and the GNOME developers. As part of Unity development Ubuntu developers had submitted API coding for inclusion in Gnome as an external dependency. According to Dave Neary, “... an external dependency is a non-GNOME module which is a dependency of a package contained in one of the GNOME module sets,” and the reasons why libappindicator was not accepted as an external dependency are that “... it does not fit that definition,” it has “... duplicate functionality with libnotify,” (the current Gnome Shell default) and its CLA does not meet current GNOME policy.[45] Mark Shuttleworth responded,

“

This is a critical juncture for the leadership of Gnome. I'll state plainly that I feel the long tail of good-hearted contributors to Gnome and Gnome applications are being let down by a decision-making process that has let competitive dynamics diminish the scope of Gnome itself. Ideas that are not generated 'at the core' have to fight incredibly and unnecessarily hard to get oxygen... getting room for ideas to be explored should not feel like a frontal assault on a machine gun post. This is no way to lead a project. This is a recipe for a project that loses great people to environments that are more open to different ways of seeing the world ... Embracing those other ideas and allowing them to compete happily and healthily is the only way to keep the innovation they bring inside your brand. Otherwise, you're doomed to watching them innovate and then having to “relayout” your own efforts to keep up, badmouthing them in the process. We started this with a strong, clear statement: Unity is a shell for Gnome. Now Gnome leadership have to decide if they want the fruit of that competition to be an asset to Gnome, or not.[46][47][48]

”

In April 2011, Mark Shuttleworth announced that Ubuntu 11.10 Oneiric Ocelot would not include the classic GNOME desktop as a fall-back to Unity, unlike Ubuntu 11.04 Natty Narwhal. Instead Ubuntu 11.10 used the Qt-based Unity 2D for users whose hardware cannot support the 3D version.[22][49] However, the classic GNOME desktop (GNOME Panel) can be installed separately in Ubuntu 11.10 and 12.04 through gnome-panel, a package in the Ubuntu repositories.[50]

At the November 2011 Ubuntu Developer Summit, it was announced that Unity for Ubuntu 12.04 would include non-re-enabling the systray, better application integration, and the ability to drag lenses onto the launcher and that the 2D version of Unity would use the same decoration buttons as the 3D version.[51]

During the planning conference for Ubuntu 12.10 it was announced that Unity 2D will likely be dropped in favour of making Unity 3D run better on lower end hardware.[23]

In July 2012, at OSCON, Shuttleworth explained some of the historical reasoning behind Unity's development. The initial decision to develop a new interface in 2008 was driven by a desire to innovate and to pass Microsoft and Apple in user experience. This meant a family of unified interfaces that could be used across many device form factors, including desktop, laptop, tablet, smart phones and TV. Shuttleworth said "‘The old desktop would force your tablet or your phone into all kinds of crazy of funny postures. So we said: Screw it. We’re going to move the desktop to where it needs to be for the future. [This] turned out to be a deeply unpopular process.”[52]

Initial testing of Unity during development was done in a laboratory setting and showed the success of the interface, despite public opposition. Real world shipping return rates also indicated acceptance. Shuttleworth explained, “ASUS ran an experiment where they shipped half a million [Unity netbooks and laptops] to Germany. Not an easy market. And the return rates on Ubuntu were exactly the same as the return rates on Windows. Which is the key indicator for OEMs who are looking to do this.”[52]

Microsoft's development of Windows 8 and its Metro interface became an additional incentive for Unity development, as Shuttleworth explained, “we [had to move] our desktop because if we didn’t we’d end up where Windows 8 is. [In Windows 8] you have this shiny tablet interface, and you sit and you use then you press the wrong button then it slaps you in the face and Windows 7 is back. And then you think OK, this is familiar, so you’re kind of getting into it and whack [Windows 8 is back].”[52]

In March 2013, the plan to use the Mir display server was announced for future development of Unity, in place of the previously announced Wayland/Weston.[38]

Early versions of Unity received mixed reviews and generated controversy. Some reviewers found fault with the implementation and limitations, while other reviewers found Unity an improvement over GNOME 2 with the further potential to improve over time.[53][54][55][56][57]

With Ubuntu 12.04, Unity received good reviews. Jack Wallen described it as an "incredible advancement". Jesse Smith described it as "attractive" and said it had grown to maturity. Ryan Paul said Unity was responsive, robust and had the reliability expected from a mature desktop shell.[58][59][60]

In reviewing an alpha version of Unity, shortly after it was unveiled in the summer of 2010, Ryan Paul of Ars Technica noted problems figuring out how to launch additional applications that were not on the dock bar. He also mentioned a number of bugs, including the inability to track which applications were open and other window management difficulties. He remarked that many of these were probably due to the early stage in the development process and expected them to be resolved with time. Paul concluded positively, “Our test of the Unity prototype leads us to believe that the project has considerable potential and could bring a lot of value to the Ubuntu Netbook Edition. Its unique visual style melds beautifully with Ubuntu's new default theme and its underlying interaction model seems compelling and well-suited for small screens.”[53][54]

In an extensive review of Ubuntu 10.10 shortly after its release in October 2010, Ryan Paul of Ars Technica made further observations on Unity, noting that "Unity is highly ambitious and offers a substantially different computing experience than the conventional Ubuntu desktop.” He concluded that "The [application] selectors are visually appealing, but they are easily the weakest part of the Unity user experience. The poor performance significantly detracts from their value in day-to-day use and the lack of actual file management functionality largely renders the file selector useless. The underlying concepts behind their design are good, however, and they have the potential to be much more valuable in the future as unity matures.”[55][56]

In March 2011, writer Benjamin Humphrey of OMG Ubuntu criticized the development version of Unity then being tested for Ubuntu 11.04 on a number of grounds, including a development process that is divorced from user experiences, the lack of response to user feedback, “... the seemingly unbelievable lack of communication the design team has,” and a user interface he described as “... cluttered and inconsistent.” Overall, however, he concluded that “... Unity is not all bad ... While a number of the concepts in Unity may be flawed from a design point of view, the actual idea itself is not, and Canonical deserve applause for trying to jump start the stagnant open source desktop with Unity when the alternatives do not evoke confidence.”[54]

On 14 April 2011, Ryan Paul of Ars Technica reviewed Unity as implemented in Ubuntu 11.04 beta, just two weeks before its stable release. At that time he reported that Unity was on track for inclusion in Natty Narwhal, despite the ambitious development schedule. He indicated, “... close attention to detail shines through in many aspects of Unity. The menubar is clean and highly functional. The sidebar dock is visually appealing and has excellent default behaviors for automatic hiding.” He did note that the interface still has some weak points, especially difficulties browsing for applications not on the dock, as well as switching between application categories. He singled out “... random packages from the repositories, which are presented as applications that are available for installation in the launcher, are distracting and largely superfluous.” Paul concluded, “There is still a lot of room for improvement, but Unity is arguably a strong improvement over the conventional GNOME 2.x environment for day-to-day use. The breadth of the changes may be disorienting for some users, but most will like what they see when Unity lands on their desktop at the end of the month.”[56] Two weeks later he added the lack of configurability to his criticisms.[61] In a very detailed assessment of Ubuntu 11.04 and Unity published on 12 May 2011, Ryan Paul further concluded Unity was a positive development for Ubuntu, but that more development must be invested to make it work right. He wrote, “They have done some incredibly impressive work so far and have delivered a desktop that is suitable for day-to-day use, but it is still very far from fulfilling its full potential.”[62]

On 25 April 2011, the eve of the release of Ubuntu 11.04, reviewer Matt Hartley of IT Management criticized Unity, saying that the "dumbing down of the Linux desktop environment is bordering on insane.”[63]

Reviewer Joey Sneddon of OMG Ubuntu was more positive about Unity in his review of Ubuntu 11.04, encouraging users, “Sure it's different — but different doesn't mean bad; the best thing to do is to give it a chance.” He concluded that Unity on the desktop makes "better use of screen space, intuitive interface layouts and, most importantly, making a desktop that works for the user and not in spite of them.”[64]

Following the release of Ubuntu 11.04 Canonical Ltd. founder Mark Shuttleworth indicated that while he was generally happy with the implementation of Unity, he felt that there was room for improvement. Shuttleworth said, “I recognise there are issues, and I would not be satisfied unless we fixed many of them in 11.10 ... Unity was the best option for the average user upgrading or installing. There are LOTS of people for whom it isn't the best, but we had to choose a default position ... It's by no means perfect, and it would be egotistical to suggest otherwise... I think the bulk of it has worked out fantastically — both at an engineering level (Compiz, Nux) and in the user experience.”[65]

In reviewing Unity in Ubuntu 11.04 on 9 May 2011, Jesse Smith of Distrowatch criticized its lack of customization, menu handling and Unity hardware requirements, saying, “There's really nothing here which should demand 3D acceleration.” He also noted that “The layout doesn't translate well to large screens or multiple-screen systems.”[66] Jack M. Germain of Linux Insider reviewed Unity on 11 May 2011, indicating strong dislike for it, saying, “Put me in the Hate It category” and indicating that as development has proceeded he likes it less and less.[67]

More criticism appeared after the release of Ubuntu 11.10. In November 2011 Robert Storey writing in DistroWatch noted that developer work on Unity is now taking up so much time that little is getting done on outstanding Ubuntu bugs, resulting in a distribution that is not as stable or as fast as it should be. Storey concluded "Perhaps it would be worth putting up with the bugs if Unity was the greatest thing since sliced bread — something wonderful that is going to revolutionize desktop computing. But it's not. I tried Unity, and it's kind of cute, but nothing to write home about.”[68]

In November 2011 OMG! Ubuntu! conducted a non-scientific poll that asked its readers "which Desktop Environment Are You Using in Ubuntu 11.10?". Of the 15,988 votes cast 46.78% indicated that they were using Unity over GNOME Shell (28.42%), Xfce (7.58%), KDE (6.92%) and LXDE (2.7%).[69]

Developers of Linux distributions based upon Ubuntu have also weighed in on the introduction of Unity in early 2011, when Unity was in its infancy. Some have been critical, including two distributions who base their criticism on usability testing. Marco Ghirlanda, the lead developer of the audio- and video-centric ArtistX, stated, “When I tried Unity on computer illiterates, they were less productive and took ages to understand the concepts behind it. When I show them how to use it, they said that it is pretty to see but hard to use.” Stephen Ewen, the lead developer for UberStudent, an Ubuntu-based Linux distribution for higher education and college-bound high school students, stated, “Unity's design decreases both visual and functional accessibility, which tabulates to decreased productivity.” Ewen also criticized Unity's menu scheme as much less accessible than on GNOME 2, which he said, “means that the brain cannot map as quickly to program categories and subcategories, which again means further decreased productivity.”[70]

Jesse Smith of DistroWatch said that many people, like him, had questioned Ubuntu's direction, including Unity. But with Ubuntu 12.04 he felt that the puzzle pieces, which individually may have been underwhelming, had come together to form a whole, clear picture. He said "Unity, though a step away from the traditional desktop, has several features which make it attractive, such as reducing mouse travel. The HUD means that newcomers can find application functionality with a quick search and more advanced users can use the HUD to quickly run menu commands from the keyboard." He wrote that Unity had grown to maturity, while telling he was bothered by its lack of flexibility.”[59]

Jack Wallen of TechRepublic - who had strongly criticized early versions of Unity - said “Since Ubuntu 12.04 was released, and I migrated over from Linux Mint, I’m working much more efficiently. This isn’t really so much a surprise to me, but to many of the detractors who assume Unity a very unproductive desktop... well, I can officially say they are wrong. [...] I realize that many people out there have spurned Unity (I was one of them for a long time), but the more I use it, the more I realize that Canonical really did their homework on how to help end users more efficiently interact with their computers. Change is hard – period. For many, the idea of change is such a painful notion they wind up missing out on some incredible advancements. Unity is one such advancement.”[58]

Ryan Paul of Ars Technica said Unity was responsive, robust and had the reliability expected from a mature desktop shell. He considered the HUD as one of several excellent improvements that had helped to make Unity "even better in Ubuntu 12.04". Yet he also wrote: “Although Unity's quality has grown to the point where it fulfills our expectations, the user experience still falls short in a number of ways. We identified several key weaknesses in our last two Ubuntu reviews, some of which still haven't been addressed yet. These issues still detract from Unity's predictability and ease of use.”[60]

One of the new features of Unity in Ubuntu 12.10 was the shopping lens. As of October 2012, it sent (through a secure HTTPS connection) the user's queries from the home lens to productsearch.ubuntu.com,[15] which then polled Amazon.com to find relevant products; Amazon then sent product images directly to the user's computer through HTTP (this changed in September 2013; see below). If the user clicked on one of these results and then bought something, Canonical received a small commission on the sale.[71]

Many reviewers criticized it: as the home lens is the natural means to search for content on the local machine, reviewers were concerned about the disclosure of queries that were intended to be local, creating a privacy problem.[15] The feature is active by default[15][71][72][73] (instead of opt-in) and many users could be unaware of it.

On 23 September 2012, Mark Shuttleworth defended the feature. He posted "the Home Lens of the Dash should let you find *anything* anywhere" and that the shopping lens is a step in that direction. He argued that anonymity is preserved because Canonical servers mediate the communication between Unity and Amazon and users could trust Ubuntu.[15][74] Ubuntu Community Manager Jono Bacon posted "These features are neatly and unobtrusively integrated into the dash, and they not only provide a more useful and comprehensive dash in giving you visibility on this content, but it also generates revenue to help continue to grow and improve Ubuntu."[75] Steven J. Vaughan-Nichols from ZDNet said the feature does not bother him and wrote "If they can make some users happy and some revenue for the company at the same time, that's fine by me."[73] Ted Samson at InfoWorld reported the responses from Shuttleworth and Bacon but still criticized the feature.[72]

On 29 October 2012, the Electronic Frontier Foundation criticized the problem. It argued that since product images were (as of October 2012) returned via insecure HTTP then a passive eavesdropper - such as someone on the same wireless network - could get a good idea of the queries. Also, Amazon could correlate the queries with IP addresses. It recommended Ubuntu developers make the feature opt-in and make Ubuntu's privacy settings more fine-grained. It noted that the Dash can be stopped from searching the Internet by switching off "Include online search results" in Ubuntu's privacy settings.[15][76]

On 7 December 2012, Richard Stallman said that Ubuntu contains spyware and should not be used by free software supporters. Jono Bacon rebuked him; he said that Ubuntu responded and implemented many of the requirements the community found important.[77][78][79]

None of Ubuntu's official derivatives (Kubuntu, Xubuntu, Lubuntu, etc.) include the feature or any variation of it.

Since September 2013, images are anonymized before being sent to the user's computer.[80]

A legal notice in the Dash informs users of the sharing of their data.[81] It states that unless the user has opted out, by turning the searches off, their queries and IP address will be sent to productsearch.ubuntu.com and "selected third parties"[71][82] for online search results. Ubuntu's Third Party Privacy Policies page informs all of the third parties that may receive users' queries and IP addresses, and states: "For information on how our selected third parties may use your information, please see their privacy policies."[15]

In March 2014, Michael Hall speaking for Canonical Ltd, indicated that in Unity 8 users will have to opt-in for each search, which will be conducted by opening a special scope and then choosing where to search. These changes would address all criticisms levelled at Canonical and Unity in the past.[83]